Heating and cooling apparatus



March 28, 1961 H. H. RHEA EI'AL 2,976,696

HEATING AND COOLING APPARATUS Filed Oct. 2, 1957 2 Sheets-Sheet 1 FIG. I

K1 HAL H.RHEA

EDWARDJBURKE INVENTORS ATTORNEY.

March 28, 1961 Filed Oct. 2, 1957 H. H. RHEA ETAL HEATING AND COOLING APPARATUS 2 Sheets-Sheet 2 FIG. 3

Off-On c Indoor Coil Fun Compressor P Outdoor Coil Fun Cool Heat J Shi:

58 FIG. 2

32. 3I HAL H. RHEA EDWARD J. BURKE INVENTORS ATTORNEY.

HEATING AND COOLING APPARATUS Filed Oct. 2, 1957, Ser. No. 687,763

4 Claims. (Cl. 62-115) This invention relates broadly to heating and cooling apparatus. More particularly, this invention relates to heating and cooling apparatus embodying a refrigeration system operable under the reverse cycle principle. Units of this type are commonly referred to as heat pumps.

Still more particularly, this invention relates to apparatus of the kind described wherein efficient removal of frost formation occurring during operation of the heat pump is achieved. In apparatus of the kind described, a compressor normally feeds hot gaseous refrigerant to a coil located outdoors or outside the area being served by the heat pump. The gaseous refrigerant is liquified in the coil and delivered to an inside coil through appropriate expansion means, where it is vaporized. The vaporous refrigerant is then transmitted to the compressor to complete the cycle. The operation described refers to the unit as it functions on the cooling cycle. In order to provide a heating effect, a four-way valve is arranged in the system so as to reverse the flow of refrigerant through the two coils and, in effect, reverse their heat transfer functions.

As indicated above, heat, on the heating cycle, is absorbed from a source such as outside or ambient air. Under those circumstances where the ambient temperature drops to a value below the freezing point of Water, a frost accumulation often occurs on the outdoor coil. The chief object of this invention is to provide an arrangement associated with the expansion valving in the refrigeration system for efficiently removing the frost which accumulates on the outdoor coil during heating cycle operation.

Another object of the invention is to provide an improved heat pump of the type described wherein a unique combination of thermal expansion valves and bypass lines are utilized to provide for the passage of refrigerant in the unit under all unit operating conditions.

Another object of the invention is to provide an improved defrosting arrangement in a heat pump of the kind contemplated, which involves temporarily reversing the operating cycle to supply hot gaseous refrigerant directly to the frost covered coil.

Other objects and features of this invention will be apparent upon a consideration of the ensuing description.

The objects of this invention are attained by providing in the system described what, in effect, are two complete sets of expansion valving. A first expansion means is arranged to feed liquid refrigerant to the outdoor coil during the heating cycle operation of the unit. A second control element is arranged to feed liquid refrigerant to the indoor coil when the unit is operating on the cooling cycle. The expansion member serving the indoor coil is provided with means for insuring passage of liquid refrigerant, during the defrosting of the outdoor coil, for vaporization therein. This arrangement prevents the compressor from drawing a low suction pressure in the suction line which, in turn, causes a low head pressure in the discharge line. By maintaining a sufficiently high head pressure in the discharge line, refrigerant having 2,976,695 Patented Mar. 28, 1961 description of the preferred embodiment of the invention,

compressor 10 forwards hot gaseous refrigerant through discharge line 11 and reversing valve 12 to an outdoor coil 13 where the refrigerant, under cooling cycle operation is liquified. This change of phase occurs as outdoor or ambient air under the influence of fan 14 is passed over the coil, extracting heat therefrom in the process. The liquid refrigerant formed in the coil 1.3

flows through a bypass line 15, controlled in turn by a check valve 16. A thermal expansion valve 17 provided to regulate liquid refrigerant flowing to the outdoor coil during the heating cycle is shown connected in parallel with check valve 16. The liquid refrigerant flows through liquid'line 18 and expansion device 19 to the indoor coil 20, which functions as an evaporator on the cooling cycle.

Bypass line 21 includes check valve 22. The function of the bypass line and check valve 22 is similar to that of bypass line 15 and check valve 16 as Will be more apparent hereinafter.

Vaporous refrigerant formed in the evaporator coil 20 passes through the four-Way valve 12 to the suction line 21' of compressor 10. A fan 23 draws indoor air over the coil 20 extracting heat therefrom in the process.

When the reversing valve 12 is actuated so that the heat pump is operating on the heating cycle, heat is extracted from the ambient air by the refrigerant flowing in coil 13. It will be obvious that under conditions of low ambient, such as occur in the northern geographical regions of the United States, the temperature of coil 13 may often drop considerably below freezing as it attempts to extract heat from ambient air having a near or below freezing temperature. Under these circumstances, a frost accumulation progressively occurs on the outdoor coil 13.

When a frost accumulation occurs on coil 13 of the magnitude sufficient to impair efiicient operation of the unit, the control system for the unit operates to temporarily reverse the four-Way valve 12 so as to cycle the unit on to cooling cycle operation for a short period of time. A control scheme of the type under consideration and which may be used with the apparatus forming the subject of this invention is disclosed in US. patent application Serial Number 531,903 filed September 1, 1955, issued June 16, 1958, as US. Letters Patent 2,847,- 833 in the name of Richard Merrick. Briefly, a timer is energized when the unit is on heating cycle and periodically closes a switch which, at a predetermined 10W outdoor coil temperature, causes a circuit, controlling energization of the four-way valve,.to be interrupted. In the event the surface or coil temperature of the outdoor coil is above a value of a level that would indicate a frosted condition on the coil, then the action of the timer is nullified. Temporary operation of the unit on the cooling cycle occurs until the outside coil temperature rises to a degree sufiicient to indicate the absence of the frost accumulation from the outside coil. Under these circumstances, the unit cycles back on the heating cycle by virtue of the operation of the control described above.

It will be appreciated that, during this temporary operation of the unit on the cooling cycle, movement of air over the indoor coil which now functions as an evaporator will provide a volume of cool air to the occupants of the enclosure being served by the heat pump. Inasmuch as the heating cycle occurs during the winter months of the year, such a condition will prove uncomfortable to occupants of the enclosure. Accordingly, when the coil is being defrosted, the fan motor is inactivated and, in effect, the evaporator coil 29 is substantially unloaded. It will be appreciated that there is a flow of air over the coil through convection. To ensure the maintenance of a suction pressure and temperature of a sufliciently high degree to maintain a relatively high temperature and pressure in the discharge line the liquid flow control member 19 shown in the form of a conventional thermostatic or thermal expansion device has provided in the valve portion 31 of the unit a passage 32 permitting flow from the liquid line 18 to the coil 20 under those circumstances when the valve itself is in closed position. Thus, means are provided for ensuring communication from the high side of the system to the low side so that the desired pressure and temperature conditions may be maintained on the low side of the system. In order to make efficient use of all the heat available in the system and, at the same time, ensure vaporization of any liquid refrigerant that might slug through to the compressor under the circumstances where the thermal expansion valve 19 is closed, the suction line is placed in communication with a source of heat, preferably from within the system itself. Referring once again to Figure 1, it will be appreciated that the suction line 21 may have a portion thereof wrapped around the compressor so as to obtain heat from this unit by conduction.

Considering the'operation of the system, particularly with respect to heating cycle operation, it will be obvious that when the unit is operated to cause a supply of warm air to be delivered to the enclosure being served by the unit, hot gaseous refrigerant flowing from the compressor will flow by line 11 to the four-way valve 12 and then on in to the indoor coil 20 functioning at this time as a condenser. Air passed over the condenser coil 20 under the influence of the fan 23 will pick up heat of liquification and supply it to the enclosure being served by the unit. Liquified refrigerant in coil 20 passes through bypass line 21 and check valve 22 to the liquid line 18. The expansion valve 19 under these circumstances will be either open or closed depending upon the type of thermal expansion valve selected. As far as this invention is concerned it is not important if the valve is open or closed because refrigerant will flow from coil 26 through the path of least resistance which happens to be line 21 .and check valve 22 whether the valve 19 is open or closed.

From the line 18 liquid refrigerant fiOWs through the thermal expansion valve 17 and into the coil 13 where it is vaporized by extracting heat from the ambient air passed thereover by fan 14. Vaporous refrigerant formed under these circumstances flows through the valve 12 to the suction line 21' through passages provided in fourway valve 12 for this operation.

As pointed out above, operation under these circumstances where a relatively low ambient temperature is encountered will cause a frost accumulation on the outside coil. The control scheme mentioned above will function automatically to detect the formation of a coating of frost on the coil sufiicient to impair eflicient operation of the unit.

With the off-on switch, note Figure 3, and the heat-cool switch closed, circuits through the compressor, four-way valve 12 and fans are completed through the upper contacts of relay 50 which assumes its position by energization of coil 51. A second circuit which includes timer controlled switch 52 is also made through coil 51. Thermostat 58 senses a predetermined low temperature in the outdoor coil sufficient to indicate the need for defrost, and opens the first circuit through coil 51. The timer is then effective to open the other circuit through coil 51, causing the relay to fall out de-energizing the solenoid. A temporary reversal of the fourway valve 12 occurs in the manner pointed out above so that hot gaseous refrigerant flowing from the compressor is directed to the coil 13 and liquified therein as heat is transferred to the frost accumulation, melting it while causing liquification of thegaseous refrigerant. Liquid refrigerant, however, flows from the coil 13 through bypass line 15 and check valve 16 to liquid line 18 because valve 17 in either its open or closed position offers more resistance to flow than valve 16. From the liquid line refrigerant flows through expansion valve 19 to the coil 2t) where it is vaporized and returned through suction line 21 to the compressor 10. However, as pointed out above, fan 23 has been inactivated so that coil 20 in effect is unloaded. Under these circumstances, the temperature and pressure in line 21' drop rapidly causing valve 19 to throttle the supply of liquid refrigerant to the coil. The drop in the suction temperature and pressure causes a corresponding drop in the temperature and pressure in the discharge line supplying hot gaseous refrigerant to coil 13 for the purpose of defrosting the coil. However, by employing a valve of the type described wherein a passage is provided in the valve seat of valve 19 sutficient to pass a supply of liquid refrigerant to coil 29 even though the thermal expansion valve 19 is in a closed position a corresponding pressure and temperature rise occurs in the suction line, which in turn causes a rise in the temperature and pressure of the refrigerant flowing to coil 13. This arrangement permits a more efficient and quicker removal of the frost from the outside coil. After the frost has been removed from the outside coil 13, the temperature of this coil rises considerably and is sensed by the thermal responsive element 58 in the control scheme illustrated in Figure 3. This condition closes a circuit through the reversing valve 12 and causes the unit to operate once again on the heating cycle with the flow of hot gaseous refrigerant being directed initially to coil 20.

It will be obvious that under these circumstances an arrangement is provided which ensures passage of refrigerant to the coil 20 when the expansion valve normally serving this coil indicates the absence of a need for the flow of refrigerant. This arrangement thus maintains a pressure and temperature in suction line 21' sufiicient to provide an adequate supply of heat for defrosting the coil 13.

Other arrangements and construction will suggest themselves to those skilled in the art, without departing from the spirit or scope of this invention.

We claim:

1. Apparatus for heating and cooling an enclosure comprising a refrigeration system including a compressor, a first heat transfer coil disposed within the area to be served by the apparatus, a second heat transfer coil disposed without the area, means for reversing the flow of refrigerant through the coils to interchange the heat transfer functions of the coils, means for passing a medium over each of said coils, and refrigerant flow control means interposed between said coils to control the flow of re frigerant between said coils, said control means including a first element for metering fiow of refrigerant to the outside coil when the outside coil functions to absorb heat from the medium passing thereover, a second element for automatically regulating flow of refrigerant to the first coil when the first coil functions to absorb heat, said second element having associated therewith means providing continuous communication between the coils.

2. In an air-to-air heat pump including a compressor, an outdoor heat transfer coil, an indoor heat transfer coil connected to form a closed circuit for the flow of refrigerant, and valve means interposed in said circuit for reversing the flow of refrigerant in a portion of the circuit to interchange the heat transfer functions of the coils; refrigerant flow control means in said circuit between said coils, said refrigerant flow control means ineluding a first flow control element for metering flow of refrigerant to the outdoor coil when the coil functions as an evaporator and a second automatically adjustable flow control element for regulating fiow of liquid refrigerant to the inside coil when the coil functions as an evaporator, said second control element being provided with an opening of a predetermined size therethrough to permit communication between the coils under all operating conditions.

3. The invention described in claim 2 wherein said automatically adjustable flow control means includes a thermal expansion valve.

4. The method of defrosting the frost accumulating coil of a heat pump including a liquification coil and frost accumulating coil and means for interchanging the heat transfer function of each coil which consists in the steps of delivering liquid refrigerant to the frost accumulating coil from the liquification coil through an expansion device for metering liquid refrigerant to the frost accumulating coil while bypassing an automatic expansion device regulating flow of refrigerant to the liquification coil when the heat transfer functionsof the coils are interchanged, reversing flow of refrigerant through said coils to supply hot gaseous refrigerant to the frost accumulating coil whereby the frost is removed from the surface of the coil and the gaseous refrigerant is liquified, and continuously supplying the liquiiied refrigerant to the liquifaction coil served by the automatic expansion device in an amount suflicient to maintain the suction temperature at a predetermined. minimum level.

References Cited in the file of this patent UNITED STATES PATENTS 2,143,687 Crago Jan. 10, 1939 2,221,062 Starr Nov. 12, 1940 2,666,298 Jones Jan. 19, 1954 2,754,661 Coyne July 17, 1956 2,823,691 Chatham 'Feb. 18, 1958 

